Jeremy Corbyn is already fighting for control of Labour just a month after becoming leader

Britain's opposition Labour Party leader Jeremy Corbyn speaks to crowds gathered at the Manchester Cathedral in Manchester, Britain October 5, 2015. REUTERS/Suzanne Plunkett On Wednesday Britain's Parliament will vote on the government's new "Charter for Budget Responsibility", a law that would stop future governments spending more than they get in tax revenue when the economy is growing.

As well as shaping the future of British economic policy, the vote is a crucial test of Labour leader Jeremy Corbyn's control over his party.

Labour shadow chancellor John McDonnell initially supported Chancellor George Osborne's new budget law. But on Tuesday he said the party would oppose it.

This has caused confusion and division within the party. Many MPs believe Labour should support the new law to help rehabilitate the party's economic image. And confusion within the party wasn't helped by the fact that even Jeremy Corbyn was apparently unaware of the shock change in policy coming from McDonnell, according to the BBC's political editor Laura Kuenssberg.

A fortnight ago, Labour told voters they were ready to back our plans. But now, they have confirmed they want to go on borrowing forever - loading debts onto our children that they can never hope to repay. This is not socialist compassion - it's economic cruelty. As Labour's Great Recession showed, those who suffer most when government run unsustainable deficits are not the richest but the poorest.

So today, with Labour's economic policy in obvious chaos, I call on all moderate, progressive Labour MPs to defy their leadership and join with us to vote for economic sanity. Failing that, they should at least follow the advice of the former shadow chancellor and abstain.

In response, former Labour Party and GMB trade union official turned Telegraph columnist Dan Hodges declared David Cameron to be the "leader of the British left."

In this context, today's vote on the budget surplus is about much more than simply economic policy. It's about control of the Labour Party.

If Jeremy Corbyn can rally his MPs to reject the surplus he will demonstrate he really is in control of a party that looks dangerously unstable at the moment, and score a blow against Osborne in the process.

But if Osborne, the Chancellor of Labour's opposition and possible next Tory leader, can inspire a revolt within the very party meant to be holding his government to account, Corbyn's authority will be seriously called into question.

It's just over a month since Corbyn was elected and already things look very tough for him.